Core composition for golf ball

ABSTRACT

A golf ball construction is provided having a solid core composition of a rubber having between 0.05 to 0.50 percent by weight of an additive selected from the group of titanium, tungsten, and combinations thereof, the additives providing an improved core composition having increased durability.

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Applications 60/304,984 and 60/304,874, each filed on Jul. 12, 2001, and which are both incorporated herein by reference. This application also relates to commonly owned U.S. application ______ having Attorney Docket No. FNT-4 filed on Jul. 12, 2002, and which is incorporated herein by reference

FIELD OF THE INVENTION

[0002] This invention is directed towards golf balls and is directed more particularly to a golf ball having a stronger, more durable core, the core containing additives which may include titanium metal or a mixture of titanium and tungsten metal.

BACKGROUND OF THE INVENTION

[0003] A significant number of conventional golf balls are made by molding a cover around a central core, a typical core having a diameter of about 1½ inches. One form of golf ball construction includes balls having a solid core. Solid core golf balls are referred to generally as “two-piece” golf balls.

[0004] The core of a two-piece golf ball is provided by molded rubber compositions that are formulated to provide a combination of hardness, high compressive strength, durability, and rebound properties. The rubber core provides resiliency to the resulting golf ball that optimizes initial impact velocity and promotes long flight distance qualities.

[0005] Polybutadiene elastomers are commonly used for the rubber component of a core and are cross linked by chemical cross-linking agents to increase the core hardness while maintaining good resiliency. Conventional elastomers and cross-linking agents are known within the art as are manufacturing processes and formulations for two-piece golf ball cores. One representative patent for a golf ball core is U.S. Pat. No. 5,508,350 which is incorporated herein by reference. Despite advances within the art, such as represented by the above referenced patent, there remains room for improvement and variation in the art directed to golf ball and golf ball core constructions, so as to improve the core properties and durability of the cores and resulting golf balls.

SUMMARY OF THE INVENTION

[0006] It is an aspect of one of the the present embodiments to provide a rubber composition formulation for a core of a golf ball useful in a two-piece golf ball.

[0007] It is yet another aspect of at least one the present embodiments to provide a rubber composition formulation for golf balls having a core comprised of a titanium metal and which may optionally include a mixture of titanium and tungsten metals.

[0008] It is yet another aspect of at least one of the present embodiments to provide a golf ball core which has between about 0.1 to about 10.0 PHR (Parts Hundred Rubber) of titanium and which has improved core durability as opposed to a core without the titanium.

[0009] It is yet another aspect of at least one of the present embodiments to provide a two-piece golf ball having a rubber core having between about 0.1 to about 10.0 PHR of a mixture of titanium and tungsten in the core composition.

[0010] It is yet another aspect of at least one of the present embodiments to provide a golf ball having improved core durability and which thereby extends the useful performance life of the resulting golf ball.

[0011] These and other features, aspects, and advantages of the present invention are provided by a golf ball core, the core having a composition comprising an elastomeric core and from about 0.05 to about 0.50 percent by weight of a particulate additive selected from the group consisting of titanium metal, tungsten metal, and combinations thereof. In one embodiment, the particulate additive is present in an amount of between about 0.05 to about 0.20 percent weight. More preferably, the particulate additive may be present in an amount of about 0.13 percent by weight.

[0012] In one preferred embodiment, the core composition includes a titanium metal having an average particle size of between about 8 to about 10 microns. The about 8 to about 10 micron titanium metal may be present in the form of a platelet. Golf ball cores constructed according to the present invention may be equipped with a cover layer to provide a finished golf ball.

[0013] These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings.

[0015]FIG. 1A is a cross section view through a two-piece golf ball illustrating the rubber core construction.

[0016]FIG. 1B is a view similar to FIG. 1A illustrating a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] Reference now will be made in detail to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the present invention are disclosed in the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions.

[0018] In describing the various figures herein, the same reference numbers may be used throughout to describe the same material, apparatus or process pathway. To avoid redundancy, detailed descriptions of much of the apparatus once described in relation to a figure is not repeated in the descriptions of subsequent figures, although such apparatus or process is labeled with the same reference numbers.

[0019] The golf ball according to the present invention may be produced from a polymer having high cis-polybutadiene rubber. Polybutadiene rubber is compounded using standard methodology including various kinds of catalysts that are well known in the art. Additional polymers, such as natural rubber, may be added and other polymers may be added or substituted as is appreciated by one having ordinary skill in the art.

[0020] Metal salts of unsaturated carboxcylic acids are used to cross link the polymers. Suitable carboxcylic acids include methacrylic, acrylic, dimethacrylic, and diacrylic acids. Suitable metal ions include sodium, potassium, magnesium, cerium, zinc, and cadmium, with zinc being preferred.

[0021] The free radical initiator included in the core composition may be selected from a variety of known polymerization initiators. Preferably, the initiator decomposes during the cure cycle. One useful initiator includes dicumyl peroxide (Luperox) as set forth in Table 2 and may be used in amounts from about 1.0 to about 5.0 parts by weight based on 100 parts elastomer.

[0022] In the present examples, zinc oxide is used as an activator as well as a filler. Zinc oxide is present in the formulation in an amount from about 3 to about 5 parts per weight based upon 100 parts elastomer. Metal salts of unsaturated carboxaylic acid such as zinc diacrylate (ZDA) may be present in an amount of about 20-40 parts by weight based upon 100 parts elastomer.

[0023] In the described formulations a titanium metal or a mixture of titanium and tungsten is introduced into the ball core polymer composition. In one embodiment, the titanium metal may be provided in the form of a fine particulate having a particle size from about 1 micron to about 15 microns. This size also correlates to mesh sizes ranging from about 200 mesh to about a 500 mesh size of the particulate. One source for a suitable titanium metal is Titanium Systems, Inc. (Townsend, Mont. USA) in which platelets of titanium having an average size of 8 to 10 microns may be obtained. As set forth in Table 2, this particular particle size of titanium metal is referred to as “New” titanium in sample TIX-4.

[0024] An additional source of titanium used in the examples TIX-2 and TIX-3, as set forth in Tables 1 and 2, provides a larger particle size titanium. This titanium has an average particle size of 45 microns and corresponds to brand name TMP-350 available from Sumitomo Sitix of Amagasaki, Inc. (Japan)

[0025] A titanium-tungsten mixture in which a tungsten particulate size of about 0.5 to 3.0 microns and a titanium particle size of about 45 microns has been found useful in the core composition. The titanium-tungsten mixture or the use of titanium metal only may be added at a range of between about 0.05 to about 0.50 percent by weight; and, in several formulations set forth in Table 2, is present at about 0.13 percent by weight. The addition of the titanium or titanium-tungsten mixture results in a core, which when used in a two-piece golf ball, provides a desirable high initial velocity, improved durability, and offers excellent properties of carry distance and total distance.

[0026] Tables 1 and 2 set forth below provide formulations for core compositions and resulting properties for cores having titanium and titanium/tungsten mixtures as listed along with appropriate controls. However, it is believed that any conventional polymer composition used for the core of a two-piece ball may be used in accordance with this invention by the addition of titanium metal or titanium-tungsten mixtures as presently taught. One having ordinary skill in the art would be able, without undue experimentation, to make adjustments to traditional fillers used in core compositions to adjust formulations to accommodate the titanium additives. As a general rule, it is desired to maintain the specific gravity of the core composition between 1.165 to 1.18 for a standard core diameter of 1.510±0.010 inches. As such, adjustments to weight fillers which may be used to bring about the reformulation. TABLE 1 TIX-1 TIX-2 TIX-3 HARDNESS HARDNESS HARDNESS NO WEIGHT COMP JIS SHORE NO WEIGHT COMP JIS SHORE NO WEIGHT COMP JIS SHORE 1 34.59 67.1 80 82 37 36 1 34.39 63.5 81 81 41 40 1 34.70 67.0 83 82 37 39 2 34.55 68.8 82 82 37 36 2 34.37 65.7 83 82 40 38 2 34.65 68.7 82 81 40 42 3 34.52 70.0 82 82 38 40 3 34.67 67.0 83 82 38 38 3 34.48 67.0 80 82 40 40 4 34.63 71.3 81 82 40 38 4 34.54 66.5 82 82 37 39 4 34.33 66.1 82 81 39 38 5 34.66 72.1 81 82 42 41 5 34.42 67.1 81 82 39 38 5 34.62 67.5 81 81 41 42 6 34.63 70.4 81 82 41 41 6 34.37 66.4 82 83 41 41 6 34.56 67.9 80 81 39 38 7 34.74 69.1 82 81 40 41 7 34.52 64.8 82 81 42 42 7 34.54 64.7 80 81 40 40 8 34.74 71.9 81 81 39 39 8 34.51 66.7 82 82 40 40 8 34.71 67.8 82 82 41 40 9 34.58 68.9 81 82 40 39 9 34.38 66.0 81 80 40 39 9 34.36 68.0 82 82 40 41 10 34.50 70.1 81 82 38 39 10 34.64 66.9 83 82 38 39 10 34.53 70.9 81 82 38 39 MAX 34.74 72.1 82 42 MAX 34.67 67.1 83 42 MAX 34.71 70.9 83 42 MIN 34.50 67.1 80 36 MIN 34.37 63.5 80 37 MIN 34.33 64.7 80 37 AVG 34.61 70.0 81.5 39.1 AVG 34.48 66.1 81.9 39.5 AVG 34.55 67.6 81.4 39.7

EXAMPLE I

[0027] In reference to Table 2, the indicated amount of a polybutadiene rubber BR1208 (Goodyear) is introduced into a Banbury or internal mixer. The recited core formulation ingredients in Table 2 are given in reference to PHR. The zinc oxide and one half of the amount of zinc diacrylate (ZDA) is added to the rubber, the initial mixture having a temperature of about 100° F. The material is blended for three minutes, during which time the temperature increases to 150° F.

[0028] Following the initial three minute interval, the remaining portion of the zinc diacrylate is added along with the barium sulphate and the corresponding amount of titanium, titanium-tungsten, or T₁O₂. Additional blending is carried out for two minutes during which time the mix temperature rises to about 170° F. At this point, the zinc stearate, aluminum silicate (Satitone), and the dicumyl peroxide (Luperox) activators are added to the polymer blend followed by additional mixing for about 1½ minutes. In place of aluminum silicate, one may use reground core material as a substitute filler. During this latter mixing step, the temperature rises to about 190° F. and care must be exercised that the temperatures do not exceed 195° F. Following the additional mixing of about 1½ minutes and prior to the elevation of the temperature to 195° F., a dump cycle is carried out in which the composition is placed into a conventional drop mill.

[0029] The drop milling process brings about an immediate reduction in temperature of the polymer composition and generates sheets of ¼ to ½ inch thick pre-form slugs of the core polymer mixture.

[0030] The resulting pre-forms of individual rubber slugs are subsequently cured by heating the compositions on the order of from about 275° F. to about 350° F. with the molding of the composition brought about simultaneously with the curing step. The molding of the composition into a core structure may be used by any conventional molding techniques such as injection, compression, or transfer molding procedures.

[0031] Following molding, the core is removed from the mold and the surface is treated by any of several techniques known in the art such as centerless grinding or surface peeling method and the like so as to facilitate adhesion of a covering composition. As set forth in Tables 1 and 2, various core composition physical properties were determined along with finished golf balls using the cores. The testing and evaluation procedures are well known to those skilled in the art.

[0032] The compression values set forth in the Tables are in the indicated weight load units. The determination of compression may be determined by a variety of mechanical apparatuses and commercially available golf compression units such as that produced by Atti Engineering Corporation of Newark, N.J. Conversion factors from a weight load determination are well known in converting a weight load compression value to PGA compression scale values.

[0033] PGA compression is generally set forth on a scale of from 0 to 200 for a golf ball with the lower values equating to a softer feel of a ball. For tournament level quality balls, compression ratings range from about 70 to about 110 and more preferably range from about 80 to 100.

[0034] The term “compression” utilized in the golf ball trade generally defines the overall deflection that a golf ball undergoes when subjected to a compressive load. The compression of the ball can affect the playability of the ball on striking and the “feel” or responsiveness of the ball during chipping and putting. The degree of compression of a ball against the club face and the softness of the cover strongly influences the resultant spin rate. In general, a softer cover will produce a higher spin rate than a harder cover. Additionally, a harder core will produce a higher spin rate than a softer core. A softer core contributes to a cover of the golf ball being under less compressive stress when struck than a harder core. As a result, the club face is not contacted to as great a degree and results in a lower spin rate.

[0035] The core is provided with at least one layer of a covering composition ranging in thickness from about 0.050 to about 0.250 inches and more preferably from about 0.060 to about 0.090 inches. The process to finish a golf ball with the cover is well known to those having ordinary skill in the art. A suitable cover as used to produce and evaluate the balls as seen in Table 1 uses a mixture of Surlyn® ionomer 8940 and Surlyn® ionomer 9910. (DuPont Corporation, Willington, Del.) The cover ionomer formulation uses ionomers 8940 and 9910 at 50 PHR respectively. Additionally, a titanium dioxide pigment is present at 3 PHR along with blue pigment at 0.04 PHR. Additional details related to the composition and construction of a golf ball cover is well known in the art and as seen in reference to U.S. Pat. Nos. 4,884,814 and 5,538,794 which are incorporated herein by reference. Additionally, it is believed that any conventional cover formulation for a two-piece ball is compatible with and would benefit from the core composition improvements noted herein.

[0036] The resulting cores produced according to the present invention provide a golf ball having a high initial velocity. Further, it has been found that the durability of the core is enhanced by the titanium additive such that the durability of the core is improved. Improved core durability will extend the useful functional life of a resulting golf ball. A degradation or failure of the golf ball core may not be immediately apparent to a golfer. Such a ball will have the same physical appearance, but will suffer a loss of initial velocity. The degradation of ball performance may be gradual and may not be immediately apparent to the user. Accordingly, cores that retain their durability extend the useful performance life of the golf ball. As indicated by the results listed in Table 2, the inclusion of various forms of titanium or titanium and tungsten combinations provide for cores which have improved durability and maintain excellent initial velocity performance. The increase in durability of finished golf balls improves the performance life of the golf ball.

[0037] As best seen in reference to FIG. 1A, one embodiment of the invention provides a golf ball 2 having a cover 6 and a core 4. The golf ball core has the titanium additive 8 uniformly distributed throughout the core composition.

[0038] An alternative embodiment for a construction of a golf ball core may be seen in reference to FIG. 1B. As seen in reference to FIG. 1B, a smaller inner core 10 is provided of a conventional core polymer mixture which does not have the titanium additive. Around this central core 10, a second core 12 may be molded from the titanium based polymer compositions as set forth and characterized in Tables 1 and 2. TABLE 2 TiX-1 TiX-2 TiX-3 TiX-4 (TiO2) (Titanium) (Ti + W) (New Ti) Reference Ball Core BR1208 100.0 100.0 100.0 100.0 100.0 ZDA 27.0 25.0 25.0 25.0 25.0 ZnO 5.0 5.0 5.0 5.0 5.0 BaSO4 8.0 13.0 13.0 13.0 13.2 TiO2 5.0 — — — — Titanium — 0.2 0.1 0.2 — Tungsten — — 0.1 — — Zinc Stearate 3.0 3.0 3.0 3.0 3.0 Satintone 5.0 5.0 5.0 5.0 5.0 Peroxide 1.3 2.4 2.4 2.5 2.0 Total 154.3 153.6 153.6 153.7 153.2 Weight(g) 34.61 34.48 34.55 34.50 34.60 Comp. 70.0 66.1 67.6 68.1 70.0 Hardness(JIS-C) 82 82 81 82 82 Hardness(SH-D) 39 40 40 40 40 Size(mm) 38.4 38.4 38.4 38.4 38.4 Ball Weight(g) 45.22 45.22 45.23 45.16 45.18 Comp. (KgF) 109.3 108.3 106.4 103.7 113.5 Hardness(JIS-C) 95 95 95 95 95 Hardness(SH-D) 64 64 64 64 64 Size(mm) 42.75 42.75 42.75 42.75 42.75 Durability(times) 187/107/119 140/132/138 91/99/124 140/156/172 80/112/137 C.O.R 0.791 0.797 0.802 0.799 0.796 Carry Dist. (yds) 244.42 244.58 244.75 247.17 247.00 Total Dist. (yds) 257.58 257.25 257.33 259.33 253.25 Initial Velocity 156.67 156.25 155.67 156.25 154.25 (mph)

[0039] As indicated in FIG. 1B, this arrangement provides an outer core region 12 which is perimeter weighted with the tungsten and/or titanium additives. As is appreciated by practioners in the art, the perimeter weighting of the core results in a golf ball having a lower spin rate. This, in turn, equates to a golf ball having a greater flight distance. It is believed that the titanium additives described above will offer similar improvements in a wide range of conventional rubber core compositions.

[0040] Using the core formulation and protocols set forth above, golf balls having solid cores were manufactured and evaluated. The balls produced were found to have a core weight of about 34.0 to 35.5 grams with a core size of 1.500 to 1.528 inches. The Atti compression values and Shore D hardness values are set forth in Tables 1 and 2. Hardness values are also provided using the JIS-C standards that are roughly twice the values of the Shore D hardness values.

[0041] The core compositions of the present invention may additionally include other conventional modifying ingredients such as fillers, conventional metal oxides, and various cross-linking agents. With respect to the amount of filler, filler amounts are primarily based upon weight restrictions and specific gravity requirements of the total polymer composition in the range from about 15 to about 30 parts by weight on 100 parts elastomer.

[0042] The coefficient of restitution (COR) of the golf balls was also determined. The COR measurements of the golf ball were made by propelling the ball horizontally at a speed of 125±5 feet per second against a generally vertical flat steel plate. The ball's incoming and outgoing velocity was electrically measured using ballistic screens as are known in the art. The ball speed was measured by timing the pulses from screen 1 to screen 2 on the way into the rebound wall and then the exit speed was timed between screen 2 to screen 1 over the same distance. Since the coefficient of restitution of a ball is related to the ball's initial velocity, it is desirable to produce a ball having a sufficiently high coefficient of restitution to closely approach the USGA limit on initial velocity.

[0043] The durability of the balls was determined by impacting the golf balls at high velocity against a steel plate. The data set forth in Table 2 sets forth the number of impacts of three different balls before a failure of the golf ball cover was noted. For the purposes of comparison it should be noted that the reference ball was a commercially available ball and had a cover composition different from the test balls TIX-1 through TIX-4.

[0044] Additional data on finished balls is provided in Table 2 are directed to the carry distance, total distance, and initial ball velocity. The distance and velocity data are derived from the average of 24 data points made using 12 balls, each ball contributing 2 of the data points. A driver having a head speed of 110 mph was used in carrying out the test. The results of the test are set forth in Table 2.

[0045] It has been found that the addition of titanium or titanium-tungsten mixtures brings about improvements in the construction of the core for a golf ball. The resulting cores have improved durability which, when incorporated into a finished golf ball, provides a longer useful life for the ball. Additionally, cores constructed as taught herein offer improved durability without sacrificing high initial velocity values.

[0046] Although preferred embodiments of the invention have been described using specific terms, devices, and methods, such description is for illustrative purposes only. The words used are words of description rather than of limitation. It is to be understood that changes and variations may be made by those of ordinary skill in the art without departing from the spirit or the scope of the present invention, which is set forth in the following claims. In addition, it should be understood that aspects of the various embodiments may be interchanged, both in whole or in part. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained therein. 

That which is claimed is:
 1. A golf ball core comprising: an elastomeric core, and, 0.05 to 0.50 percent by weight of a particulate additive selected from the group consisting of titanium, tungsten, and combinations thereof.
 2. The core according to claim 1 wherein the particulate additive is present in an amount of between about 0.05 to about 0.20 percent by weight.
 3. The core according to claim 1 wherein the particulate additive is present in an amount of about 0.13 percent by weight.
 4. A golf ball comprising: an outer cover; and, a core, the core having at least one elastomer and a particulate additive of 0.05 to 0.50 percent by weight, the additive selected from the group consisting of titanium, tungsten, and mixtures thereof.
 5. A golf ball core composition comprising: an elastomer of polybutadiene; and, about 0.05 to about 0.50 percent by weight of a titanium metal, said titanium metal having an average particle size of between about 8 to about 10 microns.
 6. The golf ball core composition according to claim 5 wherein said titanium is in the form of a platelet.
 7. The golf ball according to claim 4 wherein said particulate additive is titanium and has an average particle size of between about 8 to about 10 microns.
 8. The golf ball core composition according to claim 1 wherein said particulate additive is a mixture of a titanium metal and a tungsten metal. 